If the sector shaft adjustment is too tight, it will feel just like you describe, tight in middle, then frees up when turned. The center tooth on the sector gear is larger, so it takes more movement to turn vehicle, i.e. so its not too sensitive when straight ahead. Its a simple matter of loosening the 9/16 locknut, hold it with a wrench and back off adjustment with allen wrench. This is on top of gearbox in center of a round plate. Usually a cutout in grill to access. If you get it too loose, steering wheel will have like 3-4 inches of turning before the wheels move.Too tight, it doesn't self center after turn, and darts left/right, does not want to track straight. I tighten it (with steering straight), then back it off 1/2 a turn.
